I have heard Grana padano cheese can help, but I cannot find that cheese in my area. Other ideas?
I definitely think adding some more cheese, cream. milk or butter - dairy in general could help.
Since its a tomato-based sauce you could add more tomato sauce/tomatoes and a glug of an acid like vinegar or lemon.
Unfortunately, I don't think Grana Padano (or anything similar, like Parm, Pecorino, etc.) would reduce the heat - maybe just add another flavor to balance it a little.
Is the heat in the sauce? If so, I'd dilute with non-spicy tomato sauce, or cream (if you want a creamy sauce, of course.)
i agree. suggestion: separate sauce from meatballs; remove 1 cup sauce to small saucepan; add smooshed canned plum tomatoes, a little tomato paste; combine; heat; taste. Better? or try same but with heavy cream. a little cream in a tomato sauce can be a very nice thing. keep adding whatever worked, but to the whole batch of sauce. If nothing works, maybe someone accidentally added a jar of cayenne and you need to return it.
p.s. you can also add elements that absorb the excess cayenne, salt, sugar, whatever: white beans, cubed potatoes(raw), rice.